This invention relates to an apparatus for carrying out heat exchange between a gas and solid particulate material. More particularly, the invention relates to an apparatus designed for cooling hot particulate material such as calcined lime or cement clinker discharges from a furnace such as a rotary kiln or fluid bed reactor, or from a primary cooler such as a grate or attached tube cooler. The apparatus may also be used as a dryer or preheater for solid particulate material.
Prior to the present invention, various types of heat exchangers for gas and solid particulate material are known including reciprocating grate type coolers for hot particulate material such as cement clinker discharged from a rotary kiln; attached tube coolers for burnt lime and cement clinker discharged from a rotary kiln; and various types of shaft heat exchangers for either preheating or cooling solid particulate material. Also known are inclined type heat exchangers as shown in U.S. Pat. Nos. 4,255,130 and 4,255,131 for preheating material to be supplied to a kiln. Cross current type heat exchangers are also known and shown for example in U.S. Pat. No. 3,284,072 and U.S. patent application, Ser. No. 06/596,882 filed Apr. 5, 1984, and assigned to the assignee of the present application.
Material heat exchangers of the type which confine a bed of material between two grates have the advantage of being able to control the pressure drop of the gas across the bed of material because the depth of material can be maintained. Many prior devices of this type have the disadvantage that they are not capable of handling various size materials.
Fines will tend to migrate towards each other causing a region of decreased porosity and resultant increased pressure drop. Many devices of this type may not be able to handle oversized particles.
As gas is passed through a bed of material, fine particles will gravitate to the top. If the top of the bed of material is confined as in prior apparatus, when the fines move to the top, because the fines will be more tightly packed, there will be less space between them than between the coarse particles. This tighter spacing will cause an increase in the pressure drop across the bed of material. According to the present invention the top of the bed of material is allowed to expend to thereby eliminate the increase in pressure drop experienced by prior apparatus.